Pilger rolling mill



May 22, 1934. w. ALBERT PILGER ROLLING MILL Filed Aug. 6, 1931 4 Sheets-Sheet l .//VVENTOR MAM W WSWM 41mm,,

May 22, 1934.

w. ALBERT PILGER ROLLING MILL .4 Sheets-Sheet 2 Filed Aug. 6, 1931 Fry 22' IIYVEN TOR ZYMM um May 22, 1934. w. ALBERT 1,960,178

PILGER ROLLING MILL Fi led Aug. 6 1951 '4 Sheets-Sheet 5 Patented May 22, 1934 UNITED STATES PAT-E NT OFFICE Application August 6, 1931, Serial No. 555,587 In. Germany August 19, 1930 6 Claims.

With Pilger rolling processes as heretofore proposed, it is usual to employ a pair of rolls which,

' tween them, each roller being provided with a, circumferential groove, the central portion of which is semi-circular in cross-section and the sides of which are sloped outwardly towards the two gapswhich are located between the two rollers at the sides thereof. For a more complete understanding of this, reference may be had to the accompanying drawings in which,

Figure 1 is a diagrammatic illustration of an arrangement of Pilger rolls as heretofore known.

Figure 2 is a diagrammatic view of Pilger rolls constructed for the purpose of carrying out the process in accordance with this invention and arranged adjacent to one another,

Figure 2a is a view similar to Figure 2 illustrating a modification,

Figure 3 illustrates diagrammatically the arrangement relatively to one another of four Pilger rolling mills as heretofore employed.

Figure 4 is a view similar to Figure 3 but illustrating the arrangement of four Pilger rolls constructed in accordance with this invention,

Figure 5 is a section of a Pilger roll constructed in accordance with this invention, the section being taken at the centre of the roll in a plane at right angles to the axis of rotation thereof,

Figure 6 is a view similar to Figure 5 illustrat ing a modification of Pilger rolls constructed in accordance with this invention.

Figure 7 shows a perspective view of a Pilger roll constructed according to the invention, showing the working zones 0 and c and the compensation zone b Referring to Figure 1 it will be observed that the area between the rolls through which a tube to be rolled is arranged to pass, is divided into the following zones:--

( 1) The gap zones a and a (2) The working zones 0' and c During a rolling operation, the zones 0 and c of the rolls exert a maximum working pressure upon the tube being rolled, whilst the gap zones a and a exert a lower pressure. An initial step of a rolling operation produces thickened portions in the tubes corresponding to the gap zones a and a and prior to the next step of the 50 rolling operation, the tube is rotated through an angle of approximately 90" so that these thickened portions are rolled out by the zonesc' and c of the rolls. This process produces tubes, the walls of which vary in cross-section and are subjected to varying degrees of extension of the material thereof owing to the varying working pressures produced during each step of the rolling operation, the extension in the central portions of the zones 0 and 0 being relatively much greater than that producedin the zones a and a.

It will be appreciated that, as the thickened portions of the tube walls produced in the zones a and a in an initial step of a rolling operation are thereafter reduced in'thickness by being rolled out in the zones c and 0 a maximum extension, and consequently a maximum forward displacement of the material of the thickened portion in the direction of rolling, is effected. To this is also added the unfavorable effect of the varying circumferential speed in the calibre formed by the rolls. a

The inequalities in the working process produced in the manner described, result in the production of a relatively'large number of faulty tubes unless the tubes'produced have relatively thick walls, there being a distinct limit in thinness of tube wall which can be successfully produced by the Pilger rolling mills as above described. All efforts to produce'tubes having a wall thickness less than the limit referred to results in the production of fractures and faults in the tube walls.

This invention consists of a process for the production of seamless tubes on a Pilger rolling mill wherein each tube is rotated between successive steps in a rolling operation through a predetermined angle so that thickened portions produced in the tube wall in one step are rolledout in the next, characterized by subjecting the tube when being so rolled to at least three different zones of pressure from each roll, the pressures being arranged' to equalize substantially the spreading of the'material of the tube in relationship to the different peripheral speeds of those portions of the working surfaces of the rolls which correspond to the zones of pressure.

The defects above referred to in conjunction with knownPilger rolling mill processes are obviated by the present invention'which permits the production of tubes having a Wall thickness up to 50% less than the minimum wall thickness obtainable by the known processes referred to above.

- Referring to Figure 2, the working surface of each roll is divided into the following zones:-

(1) The gap zones a (2) The compensating zones 1) and b (3) The working zones 0, 0 c and c.

The rolling section of a pair of associated rolls ployed in accordance with Figure l hereinbefore' mentioned, provide only twice as many separate zones as the number of rolls employed, rolls constructed in accordance with this invention provide at least four times as many separate zones as the number of rolls employed.

It will be observed from Figure 2 that in addition to the already known gap zones 0. and a further compensating zones b and b are provided which exert a lesser rolling pressure than the rolls hitherto employed, as the material of the tube wall under treatment is extended to a lesser extent by the zones 1)", and b than in the zones c and c of Figure 1. In this way, the extension or spreading of the material of the tube wall produced in the zones 1) and b substantially equalizes the extension produced in the other zones.

lihe said Figure 2ashows a Pilger roll, the crossk section of which does not consist of one are but of two arcs, forminga point in the centre, producing thus a so-called pointed arc Pilger roll. Also in this arrangement there may naturally be provided besides the compensation zone formed at the top by the pointed arc form, still additional compensation zones laterally.

After an initial rolling operation by the rolls shown in Figure 2 the work is rotated through an angle of 45 so that thethicker portions of thewalls of the tubes, which have been produced in the first step of the rolling operation in the zones a, b, a b are, for example, subjected respectively, in the next successive step to the action of the zones 0, c c and c 7 Although the rolls illustrated'in Figure 2 show a relatively sharp transition from the working zones 0, c c 0 to the gap zones a and a and compensating zones bf and b, it is to beunderstoodthat the different zones may merge into one another without any sharp demarkation. Such an arrangement is illustrated in Figure 2a. A similar result may be obtained by sub-dividing the working surface of the rolls into a larger number of zones than those illustrated, in which case each working zone is located between two compensating zones or between a compensating zone and a gap zone, and if such further sub-division of the working surfaces of the rolls is employed, the angle of rotation of the rolls during each step of a rolling operation must be selected in accordance with such subdivision.

The process according to this invention may be carried out in conjunction with roller mills which employ more than'two rolls. Figure 3 illustrates diagrammatically the relative arrangement of four rolls employed in known forms of Pilger rolling mills. Each roll is provided with a centrally disposed working zone 0', c 0 or c and sloping side portions which produce the gap zones 0/, a a a, so that altogether eight separate zones are provided, that is, twice as many zones as rolls employed. An arrangement of four rolls relative to one another in accordance with this invention is illustratedin Figure 4 from which it is clear that four times as many zones are provided as rolls employed, that is to say, in the arrangement illustrated sixteen separate zones are provided as follows:

(1) Gap zones a to (1*. (2) Compensating zones b to b'*. "(3) Workingzones c to c In order to provide rolling conditions which are even more favourable for the production of thinner walls than has heretofore been possible, it is preferable, when employing theprocess according to this invention, to provide the Pilger rolls with a gripping portion 7c, Figure 5, (that portion which effects the reduction in thickness of the wall of a tube by the roll in a step in the rolling process) which extends through an angle more than one half of the angle subtended by the total working surface of the roll. This arrangement causes the reduction in wall thickness during a step in the rolling process to be distributed over a longer portion of each stretching operation and results in less material of the tube walls being forced into the gaps of the rolls, than hitherto, so that the thickening of the material in the gaps and compensating zones of the rolls is maintained within reasonable limits. The important advantages of the rolling process according to this invention, namely, uniform relative conditions between the extension of material of the tube walls and .the.

speed of the corresponding portion of the working surface of the rolls, are considerably increased by the employment of rolls formed in the manner described with reference to Figure 5.

working surface of the rolls or were portion only of said working surface.

I claim:

1. In a Pilger rolling mill, a pair of cooperating rolls having grooves therein through which the tube to be rolled passes, the surfaces of each of said grooves beingdivided into gap zones, working zones and an intermediate compensating zone, said compensating zone being a zone of reduced roller pressure and equalizing the elongation process, said zones extending circumferentially over the entire working surface of the roll.

2. In a Pilger rolling mill, a pair of cooperating rolls having grooves therein through which the tube to be rolled passes, the surfaces of each .of said grooves being divided into gap zones,

working zones and'an intermediate compensating zone, said compensating zone being a zone of reduced roller pressure and equalizing the elongation process, said zones being of uniform width and depth and extending circumferentially over the entire working surface of the roll.

3. In a Pilger rolling mill, 2. pair of cooperating rolls having grooves therein through which the tube to be rolled passes, the surfaces of each of said grooves being divided into gap zones, working zones and an intermediate compensating zone, said compensating zone being a zone of reduced roller pressure and equalizing the elongation process, said zones being of variable depth and width and extending circumferentially over the entire working surface. of the roll.

4. In a Pilger rolling mill, cooperating rolls having grooves therein defining an area through which the tube 'to be rolled passes, the surfaces of each of said grooves being divided into gap zones, a compensating zone and working zones, said zones extending circumferentially around the entire working surface of the rolls, said compensating zone being a zone of reduced roller pressure for equalizing the elongation processes and being located between working zones.

5; In a Pilger rolling mill, cooperating rolls having grooves therein defining an area through another working zone, the transition from the working zones to the compensating zone being gradual. I

6. A Pilger roll of the type described in claim 1, in which the surface that effects the reduction in thickness of the tube wall amounts to more than one half of the entire working surface.

WERNER, ALBERT. 

